COVID-19 vaccine efficacy and effectiveness

… through press releases and media, sometimes in misleading ways

… understanding the efficacy and effectiveness of vaccines is less straightforward than it might seem

… Vaccine efficacy is generally reported as a relative risk reduction (RRR)

… considers only participants who could benefit from the vaccine

… the absolute risk reduction (ARR), which is the difference between attack rates with and without a vaccine, considers the whole population

… ignored because they give a much less impressive effect size

… the number needed to vaccinate (NNV) to prevent one more case of COVID-19

… 0·9% for the Pfizer–BioNTech, 1% for the Gamaleya, 1·4% for the Moderna–NIH, 1·8% for the J&J, and 1·9% for the AstraZeneca–Oxford

… requiring access to full datasets and independent scrutiny and analyses

… 1·8 times more subjects might need to be vaccinated to prevent one more case of COVID-19 than predicted in the corresponding clinical trial

… Uncoordinated phase 3 trials do not satisfy public health requirements

… they were not designed to conclude on prevention of hospitalisation, severe disease, or death, or on prevention of infection and transmission potential